Metering valves are known in the art and have been variously utilized in a number of applications, such as public washrooms, urinals, restaurants, etc., wherever it is desired to control and meter a flow of fluid. Typically, these valves are manually actuated and permit a metered quantity of water to be dispensed before automatically shutting off. The valves are typically spring biased to a closed position with the time required for the valve to return to its closed position corresponding to the time (and thus quantity) fluid allowed to flow through the valve. The valves operate with a pressure chamber, or dashpot, wherein fluid on one side of a piston or similar member must be vented or metered to allow the piston to move to its closed position in order to shut off the valve. Various embodiments are known in the art for metering or venting the pressure chamber for this purpose.
Applicants have determined that the conventional metering valves have a significant problem in that they require periodic purging of the dashpot or pressure chamber to relieve air that eventually builds up in the chamber. If the air is not vented, the valve tends to chatter and will not properly seat in its closed position. In the past, the valves have been purged by disassembling the valve which required significant downtime for the system and excessive man hours.
U.S. Pat. No. 4,899,778 describes a metering valve whose purpose is to attain a crisp automatic shut off of the valve as opposed to a gradual shut off. The valve described includes a head portion which travels through a first segment of travel and then through a second segment of travel is at a greater rate of movement or speed than through the first segment. When the piston member moves from the open mode to the closed mode, the periphery of the piston head portion is in sliding sealing engagement with the interior surface of a first portion of a tubular unit and disengages from the interior surface of the tubular unit during the second segment of travel. The inner dimension of the second portion of the tubular unit has a greater diameter than the first portion which allows the head portion of the piston assembly to disengage from the surface. When such disengagement occurs, resistance to the piston assembly is greatly reduced which enables the piston assembly to move quickly to a fully closed position. U.S. Pat. No. 4,991,819 is similar to the '778 patent and describes internal splines or ribs defined in the interior surface of the second portion of the tubular unit which creates a non-sealing relation between the seal of the piston assembly and the head portion of the tubular unit during the second segment of travel of the piston assembly. Although the '778 patent and '819 patent teach of the desirability of quick and crisp closing of the valve, the embodiments described therein also would likely provide for venting of air entrapped above the sealing piston and, thus, are an attempt to correct the chattering problem with conventional metering valves.
The present invention relates to a relatively uncomplicated alternative solution to venting the pressure chamber which requires significantly less precision in manufacturing and machining as that proposed by the '778 and '819 patents.